1. Field of the Invention
The present invention generally relates to electro-optical readers or scanners, such as bar code symbol readers and, more particularly, to a scan module for use in applications requiring particularly compact readers.
2. Description of the Related Art
Electro-optical readers, such as bar code symbol readers, are now very common. Typically, a bar code symbol comprises one or more rows of light and dark regions, typically in the form of rectangles. The widths of the dark regions, i.e., the bars, and/or the widths of the light regions, i.e., the spaces, between the bars indicate encoded information to be read.
A bar code symbol reader illuminates the symbol and senses light reflected or scattered from the coded regions to detect the widths and spacings of the coded regions and derive the encoded information. Bar code reading type data input systems improve the efficiency and accuracy of data input for a wide variety of applications. The ease of data input in such systems facilitates more frequent and detailed data input, for example, to provide efficient inventories, tracking of work in progress, etc. To achieve these advantages, however, users or employees must be willing to consistently use the readers. The readers, therefore, must be easy and convenient to operate.
A variety of scanners is known. One particularly advantageous type of reader is an optical scanner which scans a beam of light, such as a laser beam, across the symbols. Laser scanner systems and components of the type exemplified by U.S. Pat. Nos. 4,387,297 and 4,760,248, which are owned by the assignee of the instant invention and are incorportated by reference herein, have generally been designed to read indicia having parts of different light reflectivity, i.e., bar code symbols, particularly of the Universal Product Code (UPC) type, at a certain working range or reading distance from a hand-held or stationary scanner.
A variety of mirror and motor configurations can be used to move the beam in a desired scanning pattern. For example, U.S. Pat. No. 4,251,798 discloses a rotating polygon having a planar mirror at each side, each mirror tracing a scan line across the symbol. U.S. Pat. Nos. 4,387,297 and 4,409,470 both employ a planar mirror which is repetitively and reciprocally driven in alternate circumferential directions about a drive shaft on which the mirror is mounted. U.S. Pat. No. 4,816,660 discloses a multi-mirror construction composed of a generally concave mirror portion and a generally planar mirror portion. The multi-mirror construction is repetitively reciprocally driven in alternative circumferential directions about a drive shaft on which the multi-mirror construction is mounted. All of the above-mentioned U.S. patents are incorporated herein by reference.
In electro-optical scanners of the type discussed above, a xe2x80x9cscan enginexe2x80x9d or scan module includes a laser source, optics, a scan mirror, a drive to oscillate the scan mirror, a photodetector, and associated signal processing and decoding circuitry. All of these components add size and weight to the scan module and, in turn, to the scanner. Reference may be had to U.S. Pat. Nos. 5,099,110; 5,168,149; 5,504,316; 5,262,627; 5,367,151; and 5,682,029, all owned by the assignee of the instant invention and incorporated herein by reference thereto, for details of scan modules.
In applications involving protracted use, a large, heavy, hand-held scanner can produce user fatigue. When use of the scanner produces fatigue or is in some other way inconvenient, the user is reluctant to operate the scanner. Any reluctance to consistently use the scanner defeats the data gathering purposes for which such bar code systems are intended.
Also, a need exists for compact scanners to fit into small compact devices, such as cellular telephones, personal digital assistants, notebooks, pen-shaped instruments, and ring scanners worn on the user""s finger. These devices need to be as small as possible, and the scan modules need to be made significantly smaller than would be necessary if ease of use was the only requirement.
Manufacturers of these compact devices use advanced manufacturing techniques to minimize their size. Even if no scanner is to be installed, these devices can be larger than many users would desire. When a scanner is installed in such compact devices for increased functionality, the scanning of bar code symbols is typically not the primary purpose for which the device is used. Hence, to justify its placement in the device, the scanner and the scan engine must be as small and inexpensive as possible.
Thus, an ongoing objective of bar code reader development is to miniaturize the reader as much as possible, and a need still exists to further reduce the size, weight and cost of the scan module. The mass of the moving components should be as low as possible to minimize the power required to produce the scanning movement.
It is also desirable to modularize the scan module so that a particular module can be used in a variety of different scanners. A need exists, however, to develop a particularly compact, lightweight module which contains all the necessary scanner components.
Accordingly, it is a general object of this invention to reduce the size, weight and cost of components used to produce scanning motion of the light beam, and to collect the reflected light from the indicia.
More particularly, it is an object of the present invention to develop an electro-optical scanning system which is both smaller in size and lighter in weight.
It is yet another object of the present invention to produce a scan module which is manufactured conveniently, and at a low cost.
A related object is to provide a scan module which is assembled easily.
An additional object is to reliably center the scan mirror used in such scan modules.
In keeping with the above objects and others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a scan module for use in a reader for electro-optically reading indicia. The module has a support. A generally planar base, preferably a printed circuit board, is mounted on the support. A laser light source is also mounted on the support and is operative for emitting a laser beam in a direction generally perpendicular to the base. A scan mirror is mounted on the support for oscillating movement. Optical means is mounted on the support for changing the direction of the laser beam, and for directing the laser beam to the scan mirror for reflection therefrom toward the indicia. A drive is mounted on the support for oscillating the scan mirror to sweep the laser beam across the indicia for scattering therefrom. A sensor is mounted on the support for detecting scattered light from the indicia, and for generating an electrical signal corresponding to the detected scattered light and indicative of the indicia.
Preferably, the optical means includes a fold mirror for changing the direction of the laser beam by 90xc2x0, and a focusing element and an aperture together operative for focusing the laser beam at a focus located remotely at a working distance from the scan mirror. The focusing element is mounted for movement on the support to an adjusted position, and is fixed in said adjusted position. The focusing element is mounted between the fold mirror and the scan mirror. The emission of the laser beam perpendicular to the base allows for a highly compact configuration.
Preferably, the scan mirror is mounted on a hub for joint oscillation therewith by the drive about an axis along which a shaft extends. Either the hub or the shaft may be the oscillating member. Alternatively, both the shaft and the hub may freely oscillate. The hub may be integral with the shaft which is journaled on the support in bearings having crowned thrust surfaces.
Another feature resides in magnetically centering the scan mirror. A permanent magnet is also mounted on the hub for joint oscillation with the scan mirror. The permanent magnet is a bar magnet having a magnetic axis. An energizable electromagnetic coil is mounted on the support and has an electromagnetic axis extending generally perpendicular to the magnetic axis in a rest position of the scan mirror. Energization of the coil causes magnetic fields of the coil and the magnet to interact and oscillate the hub and the scan mirror.
In accordance with this feature, the scan mirror is centered in the rest position upon de-energization of the coil, by using a pole piece having a pair of ferromagnetic portions mounted on the support and spaced apart along the magnetic axis of the permanent magnet. The poles of the permanent magnet are magnetically attracted to the ferromagnetic portions, thereby aligning the permanent magnet to the pole piece. Thus, the rest position is accurately established.
It is further advantageous where the photodetector is mounted at one surface of the printed circuit board and has surface-mounted connectors for making an electrical connection at said one surface of the printed circuit board. This allows more room for circuitry on the opposite surface of the board, since it is no longer necessary to occupy the opposite board surface with pins projecting through the board.
Thus, in accordance with this invention, the laser light source, the coil and the photodetector are all mounted at the same major surface of the printed circuit board. Signal processing circuitry for processing the electrical signal are advantageously mounted at another surface of the printed circuit board opposite to the major surface. Also, power and regulation circuitry is provided on the other surface of the printed circuit board for supplying electrical power to the laser light source, the coil and the photodetector.
The positioning of the laser light source, the focusing optis for focusing the laser beam emitted by the light source, the photodetector, the collection optics for collecting the reflected light, and the drive, especially the magnet and the coil, has been made to eliminate unused volume inside the module and to reduce the overall volume. Assembly cost is minimized by enabling standard assembly equipment, such as those being used to place components on printed circuit boards, to be employed. For example, both the coil and the photodetector can be surface mounted on the same side of the printed circuit board as the support. This leaves more space on the other side of the board to be occupied by other components.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.